In a conventional method for manufacturing tires, for example, a cap tread is formed such that rubber is extruded from an extruder onto a conveyer and is cut into a length corresponding to one tire, the cut rubber is conveyed to a forming step, and the rubber is adhered to a previously formed belt member called a first case and formed into a cylindrical shape (e.g., Patent Document 1 listed below).
There is also known a forming method in which a strip-shaped ribbon rubber extruded from an extruder is spirally wind around a forming drum and laminated into a desired shape (e.g., Patent Document 2 listed below).
There is also a method in which a plurality of dies are placed on an outer circumferential surface of a forming drum after a cylindrical base member is formed, to extrude rubber from an extruder which is adjacent to these dies, and the rubber is sandwiched under pressure between the die and the drum while rotating and driving the drum, to wind the rubber around the cylindrical base member (e.g., Patent Document 3 listed below).
According to the forming method of Patent Document 1, there is a problem that costs are increased since a cutting device for cutting rubber into a length corresponding to one tire is additionally required, and space or conveying equipment for storing and conveying the cut rubber is required in some cases.
Further, if rubber is cut using the cutting device, stress relaxation occurs around the cut portion, and dimension change is generated, which leads to deterioration in tire uniformity. Furthermore, a thickness of a joint (joint portion) between a winding start portion and a winding end portion is increased, and this may cause deterioration in tire uniformity. A level difference is generated at the joint, and this may cause incorporation of air at the time of vulcanization, or may cause a crack or peel-off at the joint.
In the method of extruding the ribbon rubber into the strip shape and spirally winding the rubber around the drum several times described in Patent Document 2, there is a tendency that cycle time becomes long. In order to avoid this, the rubber is extruded at high extruding (shearing) speed, and there is a concern that rubber burns by generation of heat.
According to the forming method of Patent Document 3, since a distance from the extruder to the die is long, a temperature of the molten rubber drops until the rubber is sandwiched, and this increases rubber viscosity. Therefore, it is difficult to sandwich the rubber between the die and the drum such that a desired rubber thickness is obtained, and there is a concern that a level difference is generated particularly at the joint.